The aim of this research was to develop a simple screening checklist to help carers and professionals know when to make a referral for a dementia assessment. A checklist was completed for all new referrals to a dementia service for people with intellectual disabilities. The obtained scores were compared to the diagnostic outcome of a comprehensive dementia assessment. The data (n = 159) indicate a higher score on the checklist correlates significantly with a subsequent diagnosis of dementia. Cut-off scores are explored. The checklist appears to be a useful tool to prompt referrals for a full dementia assessment. By helping the referrer to know when to be concerned about dementia, it may reduce the number of people referred late or not at all.